Structure and properties of rat-thymus deoxyribonucleoprotein. A comparison of the electric birefringence and other properties of deoxyribonucleoprotein prepared by various methods.

1. A comparison has been made of the properties of dNP (deoxyribonucleoprotein) prepared in various ways from rat thymus. The variables studied were: (a) extent of homogenization; (b) concentration of various metal ions; (c) concentration of EDTA; (d) extent of dialysis; (e) concentration of dNP. The chief method used for studying the dNP was that of electric birefringence; this gives information about the optical and electrical properties of molecules oriented in an electric field and about their length. 2. The extent of homogenization during the preparation affects the birefringence properties only slightly and the solubility properties of the constituent DNA not at all. However, the protein content of the dNP decreases after repeated homogenization. 3. In the presence of added Ca(2+), Mg(2+) or Na(+) an insoluble product is obtained. 4. The presence of added EDTA affects the birefringence properties only slightly. 5. In the final stage of preparation, both very limited dialysis and extensive dialysis (in terms of volume ratio) cause partial insolubility of the final product. 6. dNP prepared at low concentrations resembles in some respects dNP prepared at higher concentrations and then subjected to limited enzyme action but it is not degraded (as by extensive enzyme action); ultracentrifuge studies of the constituent DNA confirm that no degradation of the DNA has occurred. 7. It is concluded that dNP prepared at low concentrations or by extensive dialysis is denatured and that preparation of ;native' material is favoured by maintenance of a high dNP concentration and by fairly limited dialysis.